This invention relates to electromagnetic interference (EMI) shielding.
EMI shielding films block the transmission of unwanted electromagnetic energy into or out of electronic equipment. A variety of conductive materials can be used for this purpose. For applications in which it is necessary to see through the shielding (e.g., to view a display), windows containing fine wire mesh and specialized transparent films have been used. Transparent EMI shields are also described in U.S. Pat. Nos. 4,910,090 and 5,489,489 and in European Patent Application No. EP 810452. Commercially available transparent EMI shielding films typically employ a polymer substrate such as PET coated with a conductive oxide film (e.g., indium tin oxide) or with alternating coated layers of metal (e.g., silver) and conductive oxide. Representative commercially available transparent EMI shielding films include AgHT4 and AgHT8 films (CP Films, Inc.), ALTAIR(trademark) M transparent conductive film (Southwall Technologies) and AgF8 film (Chomerics Division of Parker Hannifin Corporation).
Current commercially available EMI shielding films lack adequate durability and contamination and corrosion resistance. For example, the handling guidelines for film-based shields supplied by CP Films, Inc. recommend that workers wear non-dusted latex gloves and face masks when handling shielding films; caution that the conductive film coating is susceptible to attack by inorganic ions such as sodium, potassium and chloride, all of which are present on human fingers and in saliva; and recommend that if the film does become contaminated, its surface should be cleaned with a non-linting clean room wipe dampened in isopropyl alcohol. These handling guidelines also caution against excess rubbing when wiping the coating, since it is very thin and somewhat fragile.
The present invention provides, in one aspect, a process for transparently shielding a device or enclosed area that can cause or is sensitive to electromagnetic interference, comprising at least partially surrounding the device or area with a visible light-transmissive film comprising a flexible support, an extensible visible light-transmissive continuous metal or metal alloy layer and a visible light-transmissive crosslinked polymeric protective layer, and connecting at least one grounding electrode to the metal or metal alloy layer.
In a second aspect, the invention provides an electromagnetically shielded article comprising a device or enclosed area that can cause or is sensitive to electromagnetic interference, wherein the device or area is at least partially surrounded with a visible light-transmissive film comprising a flexible support, an extensible visible light-transmissive continuous metal or metal alloy layer and a visible light-transmissive crosslinked polymeric protective layer, and at least one grounding electrode connected to the metal or metal alloy layer.
In a third aspect, the invention provides an electromagnetically shielded article comprising a device or an enclosed area that can cause or is sensitive to electromagnetic interference, wherein the device or area is at least partially surrounded with a visible light-transmissive film comprising a flexible support, and first and second extensible visible light-transmissive continuous metal or metal alloy layers separated by a visible light-transmissive crosslinked polymeric protective layer.
EMI shields made according to the invention can have increased resistance to delamination, fracture or corrosion when subjected to bending, flexing, stretching or corrosive conditions, yet still maintain good EMI shielding performance.